Electric heating unit



July 30, 1935. Q c; ABBQTT 2,009,980

ELECTRIC HEATING UNIT vOriginal Filed July 30, 1951 'Nmmmwmw 25 Inventor: Chrles C. Abbott,

His Attorweg Patented July 30, 1935 UNITED YSTATES PATENT 'oi-FICE ELECTRIC HEATING UNIT New York Original application July 30, 1931,v Serial No..

Divided and this application May 11, 1934, Serial No. 725,040

7 claimsf (c1. :w1- 67) My invention relates to electric heating units, and it has for its object the provision of an improved heating unit of this character.

My invention has special application to electric heating units wherein a resistance conductor is encased by a metallic sheath.

In one of its aspects, my invention contemplates the provision of an electric heating unit of the sheathed type having a very strong construction both mechanically and electrically. i

In accordance with my invention, I provide electrically insulating supporting members in the end portions of the sheath arranged to support the resistance conductor and its terminals. The

terminals are arranged to project from the sheath,

and in order to increase the mechanical and electrical strength of the heating unit, an insulating block is placed over the projecting portions of the terminals, this insulating member being provided with apertures for receiving the terminals. I increase the electrical strength of the terminal structure, by arranging suitable insulatl ing sleeves about the terminals where they emerge from the supporting insulator.

This application is a division of my copending application, Serial No. 554,046, led July 30, 1931.

For a more complete understanding of my invention, reference should be had to the accompanying drawing, in which Fig. 1 is an elevation of an electric heating unit arranged in accordance with my invention; Fig. 2 is an enlarged elevation in section of the heating unit of Fig. l, portions being broken away; Fig. 3 is an elevation in section of the heating unit of Fig. 1 partial'ly completed, portions being broken away; and Fig. 4 is a sectional view taken through the line 4-4' of Fig. 2 and lookingin the direction of the arrows.

Referring to the drawing, I have shown my invention in one form as applied to an electric heating unit wherein the terminals are located at the same end of the sheath. As shown, this heating unit comprises a resistance element II) supported on a suitable insulating core II. The

resistance element, as shown, preferably will. be wound on the insulating core in the form of a double helix with the'ends of the element at one end of the insulator and the mid-portion'of the conductor formed in a loop I2 at the opposite end 50 of the insulator.

The resistance conductor I0, together with the core II is supported in suitable cup-shaped insulating members I3 and I4 secured in the opposite end portions of a metallic sheath I5. These insulating members will be formed of any suitable electrically insulating material, such as green lava.

Ihe left-hand end of the sheath I5 is closed by a metallic washer-like member I6, while terminals I1 and I8 of the heater project from the 5 opposite end of the sheath. The insulating supporting member I 4 is provided with a pair of apertures in which these terminals rest and through which they pass to the exterior of the sheath, as shown in Figs. 2 and 3. These terminal 10 members, as shown, are provided with reduced portions I'Ia, I8a which pass through the apertures provided for them in the support I4 and with enlarged portions I'Ib, I8?) which rest on the inner bottom surface of the support.

The outer end portions of the terminal apertures provided in the insulator I4 are enlarged somewhat, as shown, and in these enlarged portions are placed suitable insulating sleeves 20, formed from some suitable electrically insulating material, such as sheet mica. It will be observed that these sleeves extend for a considerable distance downwardly into the insulator I4 and project for a substantial distance from the outer surface of the insulator. These sleeves 20 may be 25 secured by means of threads 2| wrapped about them and formed from some suitable material, such as asbestos.

Placed over the projecting portions of these insulating sleeves and the projecting end por# tions of the terminals is a terminal insulator 22 formed from a suitable electrically insulating material, such as porcelain. This insulator, as shown, is provided with a pair of apertures for receiving the projecting ends of the terminals, these aperv tures being enlarged to accommodate the mica sleeves 20. It will be observed that the outer ends of the ter-minal apertures provided in the support I4 and the inners ends of the apertures provided in the terminal insulator 22 are counter- 40 sunk or otherwise enlarged `to provide an annular chamber for the threads 2 I, when the insulator 22 is applied.

Suitable leads 23 are provided. These leads have secured to them suitable connector members 24 which, as shown, have threaded connections with the terminals I'I and I 8.

In order to increase the electrical strength at the terminal end of the heating unit, a suitable barrier or sheet 25, formed of a suitably electrically insulating material', such as mica, is interposed between the connectors 24. This member has a substantially triangular shape, as shown in Figs. 2 and 4, the base of the triangle being received in a suitable transverse slot 26 provided 22 aooaeso for it inthe insulator 22 and the apex being secured against lateral displacement by means of a suitable asbestos thread 2l wound about the adjacent portions of the leads 23.

A suitable terminal protective casing 28 is threaded on the terminal end of the unit, as shown in Figs. l and 2.

The conductor and those portions of the terminals within the sheath are surrounded by a compacted, powdered, heat refractory, electrically insulating material 23, such as powdered magnesium oxide.

In forming the heating unit, the resistance con-v ductor I@ is wound so as to form the double helix, previously described, in any suitable manner, as on any suitable arbor, and then is assembled with the insulating core Il.

The terminal members Il and I6 are then secured to the ends of the resistance conductor. The end portions of the resistance conductor are reduced somewhat, as shown in Fig. 2, and holes provided for them in the terminals are shaped accordingly. This arrangementis advisable in order to strengthen the terminals at their threaded portions. The terminals are secured to the resistance element I6 in any suitable manner, but preferably in the manner described and claimed in my copending application, Serial No. 628,693, :tiled August 13, 1932, which application is a division of my above-mentioned copending application, Serial No. 554,046.

After the terminals have been secured to the conductor, the conductor is assembled with its insulating supporting member I t. This supporting member and the assembled resistance conductor is then inserted in the metallic sheath I5. The sheath is prepared for the insertion of the resistance element and its supporting insulator Ill by reducing one of its ends, such for example as theright-hand end as viewed in Fig. 3, and by providing in this end a head piece 30. This head piece is provided with a pair of apertures for receiving the two terminals I'I and I8, and each aperture is counter-bored at its outer end, as shown in Fig. 3. The head piece 3D is secured to the sheath by a spun-over portion 3 I.

Suitable `metallic sleeves 32 with reduced ends to t into the counterbores provided about the openings in the head piece are then arranged over the projecting ends of the terminals and are secured thereon by means of nuts 33, these nuts being turned inwardly on the threaded portions of the terminals to draw the terminals and supporting member I4 snugly up against the head piece.

' I'he supporting insulator I3 is then inserted in the other end of the' sheath and over this insulator is inserted a loading Washer 34 towhich the loop I2, formed in the resistance coil, is secured by means of a suitable thread or wire 35 (Fig. 3). This thread or wirev passes through a pair of apertures in the loading washer and is drawn tight and secured to the washer so as to place the resistance coil under a slight tension. It will be understood that the loading washer will be received in a suitable counterbore 38 prothe sheath then being spun over as indicated in Fig. 2.to secure the washer I3. Preferably and as shown, this washer Will be provided with a slight recess in its outer surface so that during the subsequent reducing or swaging operation, the plate I 6 will tend to bulge inwardly rather than outwardly.

To swage the sheath, the entire unit is passed through a swaging machine, the swaging operation reducing the diameter and increasing the length of the unit. Several passes through the swaging machine usually are necessary, and if desired, the heating unit maybe annealed between successive swaging operations in order to prevent the resistance element and sheath from becoming hard and brittle. It will be understood that the unit will be swaged sufficiently to compact the magnesium oxide to a hard dense mass about the resistance element and terminals.

The sheath is then provided with exterior threads on its terminal end for the reception of the protective casing 28.

After this, the mica insulating sleeves 2U are inserted in the counterbores provided for them in the supporting insulator It and are secured by means of the threads 2i. Then the terminal insulator 22 is assembled.

The leads 23 are then attached to the terminals by the connector members 25. The connector members, as shown (Fig. 2), are threaded on their associated terminals Il' and I8. After the connectors are screwed on, they are brazed to the associated terminals by means of a suitable brazing material Q0, such as silver solder, through apertures 5I, provided in the connectors. This brazing material insures the electrical connection between the resistance element and its supply lead. The connections between the connectors 24 and the leads 23 and between the connectors and terminals are described and claimed in my abovementioned copending application, Serial No.`

After the leads are thus attached, the triangular mica barrier or sheet 25 is assembled. It will be understood that the terminal insulator 22 will have been provided with the transverse slot 26 for receiving the base of the sheet 25; the apex of the sheet will then be secured by wrapping the asbestos thread 2T about the leads 23.

The terminal protective' casing 28 is then screwed on the sheath and is further secured by a set screw 42, as shown.

The opposite end of the sheath may be closed by a suitable plate d3 arranged over the washer I6, as shown. y

The terminal insulator 22, together with the insulating sheet 25 provides avery strong electrical terminal arrangement for the heater.

While I have shown a particular embodiment of my invention, it will be understood, of course,

that I do not wish to be limited thereto since manyV modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modications as fall within the true spirit and scope of my invention. l

What I claim as new anddesire to secure by Letters Patent in the United States is:

1. An electric heater comprising a metallic sheath, a resistance conductor within said sheath, a supporting insulator for said resistance conductor mounted Within said sheath, said insulator` having an aperture therethrough, a terrminal member for said resistance conductor mounted within said aperture and having a portion projecting therefrom on the exterior of said sheath, an insulating sleeve surrounding the portion of said terminal emerging from said supporting insulator, said insulator having a recess for receiving the inner end portion of said sleeve, and an insulating block on the exterior of said sheath having a recess receiving the exterior portion of said insulating sleeve and an. aperture through which said terminal is passed.

2. An electric heater comprising a metallic sheath, a resistance conductor Within said sheath, said conductor having its ends adjacent each other at one end of said sheath, a supporting insulator for said conductor mounted within the said one end of said sheath, said insulator being provided with apertures extending therethrough and having enlarged portions opening to the exterior oi said sheath, terminal members secured to said conductor ends and passed through said apertures to the exterior of said sheath, insulating sleeves received in the enlarged portions of said apertures so as to surround the portions of said terminals emerging from said insulators, an insulating block on the exterior oi said sheath having recesses for receiving said insulating sleeves and apertures through which said terminals are passed, lead connectors secured to the ends of said terminals and an insulating sheet interposed between said connectors.

3. An electric heater comprising a metallic sheath, an insulating core, a resistance conductor Wound on said core to form a double helix with its end portions at one end of said core, spaced cup-shaped insulating supporting members in said sheath for receiving the end portions of said coiled resistance element, terminals secured to the ends of said resistance element, the cup support at the terminal end being provided with aperturesthrough which said terminals are passed to the exterior of said sheath, insulating sleeves in said apertures surrounding said terminals and an insulating block on the exterior of said sheath provided with apertures through which said terminals are projected.

4. An electric heater comprising a metallic sheath, a resistance conductor Within said sheath, a supporting insulator for said resistance conductor mounted within said sheath, said insulator having an aperture therethrough, a terminal member for said resistance conductor mounted Within said aperture and having a portion projee-ting therefrom on the exterior of said sheath,

an insulating sleeve surrounding the portion of said terminal emerging from said supporting insulator, a thread-like member surrounding said insulating sleeve so as to secure it to said terminal, said insulator having a recess for receiving the inner end portion of said sleeve, and an insulating block on the exterior of said sheath having a recess receiving the exterior portion oi said insulating sleeve and an aperture through which said terminal is passed, said recesses in said insulator and said insulating block having iiared portion at their adjacent ends arranged to define a chamber for receiving said thread-like member. 5. An electric heater comprising a metallic sheath, a resistance conductor Within said sheath, a supporting insulator for said resistance conductor mounted Within said sheath, said insulator having an aperture therethrough, a metallic head piece in said sheath etvfeen the end thereof and said insulator, said head piece being provided with an aperture aligned with the aperture in said insulator, means securing said head piece in said sheath, a terminal member for said resistance conductor mounted Within said apertures and having a portion projecting from said head piece on the exterior of said sheath, an insulating sleeve surrounding the portion of said terminal. emerging from said supporting insulator, said insulator having a recess for receiving the inner end porn tion of said sleeve, and an insulating block on the exterior of said sheath having a recess receiving the exterior portion or" said insulating sleeve, and an aperture through Which said terminal is passed.

6. An electric heater comprising a metallic sheath, a resistance conductor Within said sheath, said conductor having its ends adjacent each other at one end of said sheath, a supporting insulator vfor said conductor mounted within the said one end of said sheath, said insulator being provided With apertures extending therethrough and having enlarged portions opening toward the exterior of said sheath, terminal members secured to said conductor and passedthrough said apertures to the exterior of said sheath, insulating sleeves received in the enlarged portions of said apertures so as to surround the portions of said terminals emerging from said insulators, an insulating block on the exterior of said sheath having recesses for receiving said insulating sleeves and apertures through which said terminals are passed, lead connectors secured to the ends of said terminals, a triangular shaped insulating sheet interposed between said connectors, said insulating block having a recess for receiving the base of said triangular sheet and a thread-like member secured to said connectors around the apex of said triangular sheet.

7. An electric heater comprising a metallic sheath, a resistance conductor in saidlsheath, a supporting insulator for said resistance conduc tor mounted within said sheath, said insulator having an aperture therethrough, a terminal member for said resistance conductor mounted within said aperture having a portion projecting therefrom on the exterior of said sheath, layers of insulating material surrounding the portion of said terminal projecting from said sheath and a portion of said terminal Within said insulator, said insulator having a recess for receiving the insulating layer surrounding said latter terminal portion.`

CHARLES C. ABBOTT.

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